Memory and CPU's are about it.
GPU's have all shifted to bespoke hardware that is physically impossible to run on consumer hardware platforms. All the Blackwell etc type chips are insanely dense. Most GPU's built for datacenter use don't even have video output hardware so it's somewhat useless.
Memory (DIMM's) are somewhat standard. Most servers use registered ECC which doesn't work in consumer platforms, but the actual memory chips themselves could be removed and replaced onto normal consumer DIMM's as they are basically univsersal.
x86 CPU's are still CPU's at least. You might need weird motherboards but those can still be run by us plebs.